Corrosion resistant metal



Patented Jan. 29, 1946 4 I v UNITED "STATES PATENT OFFICE CORROSION RESISTANT METAL Robert M. Thomas, Pasadena, Calil'., and Charles W. Ostrander, Baltimore, Md., asslgnors to Rheem Research Products Incorporated, Baltimore, Md., a corporation of New York No Drawing. Application March 21, 1945,

I Serial No. 584,038

5 Claims. (01. .14s-c) This invention'relates to a treatment for imformic acid, but the latter is D While parting a visible corrosion resistant coating to sulfuric acid is pref rr sol le lf tes such zinc, cadmium and their alloys. The invention is as copper sulfate, ferric sulfate or zinc sulfate may useful in connection with surfaces coated with be used. Cobalt nitrate or nitric acid may be these metals, their alloys, a well as castings of utilized instead of the preferred zinc nitrate.

the same and galvanized metal. Where such alternative constituents are em- The primary object of the invention is to proployed, they are used in amounts to produce a duce an improved corrosion resistant coating havsolution having substantially the same characing an attractive bronze appearance. teristics, 'properties and preferred content of Another object of the invention is to provide chemicals as the preferred dip above set forth. an aqueous acidic solution mixture to which the The formic acid or salt thereof together with metal may be subjected, as by immersion, and the dichromate reacts with the metal surface to the desired coating produced economically with forma coating. The nitric acid or nitrate renders respect to amounts of chemicals required and in th visible coating produced by the reaction of acommercially feasible time cycle. l5 the dichromate and formic acid homogeneous A further Object o the i i n is to provide and uniform in ap earance. The function of the a solution containing components which are critisulfuric acid or sulfate in the foregoing composical to produce the coating, namely chromic acid tion is primarily 'to modify the color of the coator soluble salts thereof, formic acid or soluble ing to give an attractive and bronze effect. salts thereof, nitric acid or its soluble salts and We claim:

sulfuric acid or a soluble sulfate. 1. A method of producing an adherent cor- In carrying out the invention, a suitable solurosion resistant coating on zinc and cadmium, tion mixture as indicated below is prepared, and comprising subjecting the same to an aqueous the metal or alloyto be coated is dipped therein acidic solution essentially consisting of a water or subjected to the solution in any appropriate soluble chromium compound selected from the manner to form the coating. group consisting of chromic acid and its salts and Example an organic compound which is easily oxidized by chromic acid and selected from the group con- Naacmo" 59 sisting of formic acid and soluble formates, a HCOOH "cubic centimeters liter" 39 compound selectedfrom the group consisting of Zn(NOs)2 gra s e i nitric acid and soluble salts thereof, and a com- Hzso "cublc centlmeters per hter" 5 pound selected from the group consisting of sul- Initially, the solution has a pH of about 1.0 to furic acid and soluble salts thereof, until a visible 1.1 and may be satisfactorily used through a pH coating is formed, the amount of the organic comof about 3.4. Acoating is formed at al1tempera- 5 pound being 5111350181111 t0 Cause the Chromium tures between about 33 F, and 212 F, but w compound in conjunction with the organic comprefer to operate at about 80 t 90 F, In fiv pound to produce a visible corrosion resistant seconds, a light bronze slightly iridescent coat- Chromium o t ining coati g on e e metal,

mg is produced, while in twenty seconds a darker the compo d selected fr h r p consisting bronze coating is formed. 7 of sulfuric acid and soluble salts thereof being in The dichromate is used inthe range between amount sufficient to produce a bronze color.

, substantially 30 g./l. and '70 g./l., the formic acid 2. The process in accordance with claim 1 is used in the range between about 30 cc./l. and wherein the aqueous acidic solution essentially 60 cc./l.; the zinc nitrate is used in amount of consists of NazCrzO'z, HCOOH, Zn(NO3)2 and from about 10 g./l. to 30 g./1., and the sulfuric H2804 until a visible corrosion resistant coating acid is used in amount of from about 4 to 10 cc./l. having a bronze color is formed.

The foregoing conditions have been found to 3. The process in accordance with claim 1 be preferable for producing an improved visible wherein the solution has an acidity of about pH corrosion resistant coating of a pronounced and o a u pH 34 a d a t p r re of from attractive bronze color. Instead of a dichromate about 33 F. toabout 212 F.

which is preferred, chromic acid or soluble salts 4. An aqueous acidic solution for imparti of chromic acid, notably sodium and potassium bronze colored corrosion resistant coating to zinc chromatc, may be used. A suitable soluble salt and cadmium and alloys thereof, said solution of formic acid may be employed such as sodium, essentially consisting of a water soluble chromium potassium or ammonium formate in lieu of compound selected from the group consisting of chromic acid and its salts and an organic compound which is easily oxidized by chromic acid and selected from the group consisting of formic acid and soluble formates, a compound selected from the group consisting of nitric acid and soluble salts thereof, and a compound selected from the group consisting of sulfuric acid and soluble salts thereof, the amount of the organic compound being sufllcient tocause the chromium compound in conjunction with the organic com- 10 pound to produce a visible corrosion resistant chromium containing coating on the base metal, the compound selected from the group consisting of sulfuric acid and soluble salts thereof being in amount sufllcient to produce a bronze color.

5. An aqueous acidic solution in accordance with claim 4 which consists essentially of NazCrzOv, I-ICOOH, Zn(NO3) z and H2304. ROBERT M. THOMAS. CHARLES W. OS'I'RANDER. 

